1. Field of the Invention
The invention relates generally to a haemolysator, and in particular, a haemolysator in combination with a cuvette (measuring chamber) for receiving a sample. The invention also relates to a spectroscopic analyzer comprising a haemolysator. Furthermore, the invention relates to an oscillation system comprising multilayer actuators and in particular to a haemolysator comprising multilayer actuators. The invention also relates to a process for the function testing and monitoring of the operating state of a haemolysator equipped with piezoelectric multilayer actuators.
2. Description of Related Art
A haemolysator as initially mentioned is used in a spectroscopic analyzer, in particular for the spectroscopic determination of haemoglobin derivatives, e.g., O2Hb, HHb, COHb, MetHb and quantities derived therefrom (oximetry and co-oximetry, respectively). However, the haemolysator is also suitable for use in combined spectroscopic-chemical analyzers. Said analyzers serve, among other things, for the decentralized determination of blood gases (O2, CO2, pH), electrolytes (K+, Na+, Ca++, Cl−), metabolites (glucose and lactate), haematocrit, haemoglobin parameters (tHb, SO2, etc.) and bilirubin in whole-blood samples. In doing so, characteristic photometric absorption properties of those substances are utilized and measured values are evaluated via a mathematical algorithm.
In order to be able to achieve the required measuring accuracy, a haemolysis of the whole blood is necessary prior to the optical measurement, which haemolysis is performed by means of the haemolysator. In doing so, the blood cells are destroyed mostly by ultrasonic energy in order to be able to conduct the measurement without interfering light scattering effects.
In FIG. 1, a schematic diagram of an oximeter module 200 of a spectroscopic analyzer is illustrated, with the oximeter module being known from the prior art. Said oximeter module comprises a source of measuring light 201 which generates a beam of light 202 which is concentrated by a lens 203 and directed onto an optical measuring chamber 204. Said optical measuring chamber 204, which is also referred to as a “cuvette”, has transparent case walls through which the beam of light 202 can pass. A sample 205, in particular a whole-blood sample, having characteristic photometric absorption properties which change the spectral composition of the beam of light 202 passing through the sample is located in the measuring chamber 204. After leaving the measuring chamber 204, the beam of light 202 is introduced into an optical waveguide 206 and guided to a spectroscopic sensor 207. The spectroscopic analysis of the sample 205 requires a haemolysis in which the blood cells in a whole-blood sample are destroyed by ultrasound so that the sample is transformed into a liquid which does not substantially scatter the beam of light 202. The haemolysis is performed by means of a haemolysator 210 desiged as an ultrasonic transducer and comprising piezoceramic elements 211 which generate mechanical oscillations via excitation by electrical alternating current signals due to the reverse piezo effect (i.e., the physical phenomenon in which mechanical deformations are caused by applying electrical signals to a piezo element), which mechanical oscillations are transmitted to a resonator 212 and amplified (see also FIG. 2). The resonator 212 in turn transmits the mechanical oscillations via a coupling surface 213 formed on its front side to a case wall of the measuring chamber 204, whereby the oscillations propagate into the sample 205 and cause the blood cells to burst therein due to cavitation effects. Furthermore, the haemolysator 210 has a counter weight 214 arranged on the side of the piezoceramic elements 211 which faces away from the resonator 212. In order that the measuring chamber 204 is not destroyed by the mechanical oscillations and in order to ensure an appropriate propagation of the mechanical oscillations into the sample 205, the measuring chamber must be mounted elastically. This is effected by a spring washer 215 which prestresses an anvil 216 against the side of the measuring chamber 204 which faces the haemolysator 210.
According to the prior art, haemolysators 210 of the ultrasonic transducer type have so far been configured as resonance oscillators which are prompted to oscillate by an electrical sinusoidal signal at the resonance frequency inherent to the haemolysator. The ultrasonic transducer haemolysator 210 illustrated in FIG. 2 is such a prior art haemolysator 210 based on the resonance oscillator principle.
Spectroscopic analyzers comprising haemolysators according to the resonance oscillator principle are known, for example, from U.S. Pat. No. 3,972,614.
A disadvantage of known haemolysators of the resonance oscillator ultrasonic transducer type is their considerable overall length which has to be dimensioned such that a maximum oscillation amplitude is achieved in the sample position. The resonance oscillator ultrasonic transducer is a λ/2-oscillator which requires an overall length of a few cm (typically approx. 10 cm). This results in bulky analyzers.
Furthermore, the resonance oscillator must have a very high quality because of its action principle of excitation at resonance frequency, which leads to the fact that it can be operated only in an extremely narrow frequency range. Firstly, this limits the control possibilities of the haemolytic process, since cavitation bubbles of different sizes and densities develop in the blood sample depending on the ultrasonic frequency. Secondly, in case of replaceable measuring chambers (cuvettes) in which haemolysis is to be performed, the problem which arises is that of different material and oscillation properties which are variable throughout the lifetime. If mechanical oscillations are transmitted by a resonance oscillator ultrasonic transducer—which, due to its principle, has been adjusted to a fixed frequency—the result will be that maladjustments might occur in the frequency behaviour, which would result in an insufficient haemolysis of the blood sample in the cuvette. Thirdly, it would also be beneficial to be able to perform quality controls and system tests during operation, but resonance oscillators with their very narrow useful frequency range are likewise unsuited for this.
Finally, the relatively high energy consumption of known resonance oscillator ultrasonic transducers is also problematic.
Accordingly, the inventors have identified a need in the art to provide a haemolysator for an oximeter module of a spectroscopic analyzer which is small and quiet, has a low energy consumption of <=15 W continuous power, can be subjected to internal quality checks, allows the system to remain operable even if the cuvette is exchanged, which changes the oscillation properties of the system, and performs a complete haemolysis of the blood sample.